Generally, the brushless AC generator for a vehicle of this type is arranged, as disclosed in Patent Reference 1, for example, so that a cylindrical casing formed by uniting a pair of brackets would contain component members such as a rotating shaft, a rotor, a ring-shaped excitation coil and a ring-shaped stator coil to generate an air flow along the component members by means of an external fan provided in the rotating shaft outside the bracket and to cool the air flow.    Patent Document 1: JP-A-2001-211608